Close the above question - my son fixed my problem. With the message open I was clicking on More and then Print. Apparently, that is not the correct place to do the print request. It needs to be done from the area where the lines appear near the upper right corner. My son moved an icon for the correct print command to the task bar for me and not it all works just fine.

I was hopeful about that solution, but was disappointed in the end. Fact is that I had no problem up to two weeks ago and it's emails only that won't print. They just go on the print queue and stay there. I tried saving the file as a .prn but then Acrobat couldn't open it, saying it may not have been properly decoded. Worked around it by copying the text of the message to a blank Word document. That worked fine, but doesn't seem the right way to go Thunderbird!